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<h2><span class="refentrytitle"><a name="gio-GPollableOutputStream.top_of_page"></a>GPollableOutputStream</span></h2>
<p>GPollableOutputStream — Interface for pollable output streams</p>
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<div class="refsynopsisdiv">
<a name="gio-GPollableOutputStream.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis">
#include &lt;gio/gio.h&gt;

                    <a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream">GPollableOutputStream</a>;
struct              <a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStreamInterface" title="struct GPollableOutputStreamInterface">GPollableOutputStreamInterface</a>;

<a href="../glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            <a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-can-poll" title="g_pollable_output_stream_can_poll ()">g_pollable_output_stream_can_poll</a>   (<em class="parameter"><code><a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> *stream</code></em>);
<a href="../glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            <a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-is-writable" title="g_pollable_output_stream_is_writable ()">g_pollable_output_stream_is_writable</a>
                                                        (<em class="parameter"><code><a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> *stream</code></em>);
<a href="../glib/glib-The-Main-Event-Loop.html#GSource"><span class="returnvalue">GSource</span></a> *           <a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-create-source" title="g_pollable_output_stream_create_source ()">g_pollable_output_stream_create_source</a>
                                                        (<em class="parameter"><code><a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> *stream</code></em>,
                                                         <em class="parameter"><code><a class="link" href="gio-GCancellable.html#GCancellable" title="GCancellable"><span class="type">GCancellable</span></a> *cancellable</code></em>);
<a href="../glib/glib-Basic-Types.html#gssize"><span class="returnvalue">gssize</span></a>              <a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-write-nonblocking" title="g_pollable_output_stream_write_nonblocking ()">g_pollable_output_stream_write_nonblocking</a>
                                                        (<em class="parameter"><code><a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> *stream</code></em>,
                                                         <em class="parameter"><code>const <span class="type">void</span> *buffer</code></em>,
                                                         <em class="parameter"><code><a href="../glib/glib-Basic-Types.html#gsize"><span class="type">gsize</span></a> size</code></em>,
                                                         <em class="parameter"><code><a class="link" href="gio-GCancellable.html#GCancellable" title="GCancellable"><span class="type">GCancellable</span></a> *cancellable</code></em>,
                                                         <em class="parameter"><code><a href="../glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> **error</code></em>);
</pre>
</div>
<div class="refsect1">
<a name="gio-GPollableOutputStream.description"></a><h2>Description</h2>
<p>
<a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> is implemented by <a class="link" href="gio-GOutputStream.html#GOutputStream" title="GOutputStream"><span class="type">GOutputStream</span></a>s that
can be polled for readiness to write. This can be used when
interfacing with a non-GIO API that expects
UNIX-file-descriptor-style asynchronous I/O rather than GIO-style.
</p>
</div>
<div class="refsect1">
<a name="gio-GPollableOutputStream.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="GPollableOutputStream"></a><h3>GPollableOutputStream</h3>
<pre class="programlisting">typedef struct _GPollableOutputStream GPollableOutputStream;</pre>
<p>
An interface for a <a class="link" href="gio-GOutputStream.html#GOutputStream" title="GOutputStream"><span class="type">GOutputStream</span></a> that can be polled for readability.
</p>
<p class="since">Since 2.28</p>
</div>
<hr>
<div class="refsect2">
<a name="GPollableOutputStreamInterface"></a><h3>struct GPollableOutputStreamInterface</h3>
<pre class="programlisting">struct GPollableOutputStreamInterface {
  GTypeInterface g_iface;

  /* Virtual Table */
  gboolean     (*can_poll)          (GPollableOutputStream  *stream);

  gboolean     (*is_writable)       (GPollableOutputStream  *stream);
  GSource *    (*create_source)     (GPollableOutputStream  *stream,
				     GCancellable           *cancellable);
  gssize       (*write_nonblocking) (GPollableOutputStream  *stream,
				     const void             *buffer,
				     gsize                   size,
				     GError                **error);
};
</pre>
<p>
The interface for pollable output streams.
</p>
<p>
The default implementation of <em class="parameter"><code>can_poll</code></em> always returns <a href="../glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a>.
</p>
<p>
The default implementation of <em class="parameter"><code>write_nonblocking</code></em> calls
<a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-is-writable" title="g_pollable_output_stream_is_writable ()"><code class="function">g_pollable_output_stream_is_writable()</code></a>, and then calls
<a class="link" href="gio-GOutputStream.html#g-output-stream-write" title="g_output_stream_write ()"><code class="function">g_output_stream_write()</code></a> if it returns <a href="../glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a>. This means you only
need to override it if it is possible that your <em class="parameter"><code>is_writable</code></em>
implementation may return <a href="../glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> when the stream is not actually
writable.
</p>
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<td><p><span class="term"><a href="../gobject/gobject-Type-Information.html#GTypeInterface"><span class="type">GTypeInterface</span></a> <em class="structfield"><code><a name="GPollableOutputStreamInterface.g-iface"></a>g_iface</code></em>;</span></p></td>
<td>The parent interface.</td>
</tr>
<tr>
<td><p><span class="term"><em class="structfield"><code><a name="GPollableOutputStreamInterface.can-poll"></a>can_poll</code></em> ()</span></p></td>
<td>Checks if the <a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> instance is actually pollable</td>
</tr>
<tr>
<td><p><span class="term"><em class="structfield"><code><a name="GPollableOutputStreamInterface.is-writable"></a>is_writable</code></em> ()</span></p></td>
<td>Checks if the stream is writable</td>
</tr>
<tr>
<td><p><span class="term"><em class="structfield"><code><a name="GPollableOutputStreamInterface.create-source"></a>create_source</code></em> ()</span></p></td>
<td>Creates a <a href="../glib/glib-The-Main-Event-Loop.html#GSource"><span class="type">GSource</span></a> to poll the stream</td>
</tr>
<tr>
<td><p><span class="term"><em class="structfield"><code><a name="GPollableOutputStreamInterface.write-nonblocking"></a>write_nonblocking</code></em> ()</span></p></td>
<td>Does a non-blocking write or returns
<a class="link" href="gio-GIOError.html#G-IO-ERROR-WOULD-BLOCK:CAPS"><code class="literal">G_IO_ERROR_WOULD_BLOCK</code></a>
</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 2.28</p>
</div>
<hr>
<div class="refsect2">
<a name="g-pollable-output-stream-can-poll"></a><h3>g_pollable_output_stream_can_poll ()</h3>
<pre class="programlisting"><a href="../glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            g_pollable_output_stream_can_poll   (<em class="parameter"><code><a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> *stream</code></em>);</pre>
<p>
Checks if <em class="parameter"><code>stream</code></em> is actually pollable. Some classes may implement
<a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> but have only certain instances of that
class be pollable. If this method returns <a href="../glib/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a>, then the behavior
of other <a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> methods is undefined.
</p>
<p>
For any given stream, the value returned by this method is constant;
a stream cannot switch from pollable to non-pollable or vice versa.
</p>
<div class="variablelist"><table border="0">
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<td><p><span class="term"><em class="parameter"><code>stream</code></em> :</span></p></td>
<td>a <a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a>.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>
<a href="../glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> if <em class="parameter"><code>stream</code></em> is pollable, <a href="../glib/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> if not.</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 2.28</p>
</div>
<hr>
<div class="refsect2">
<a name="g-pollable-output-stream-is-writable"></a><h3>g_pollable_output_stream_is_writable ()</h3>
<pre class="programlisting"><a href="../glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            g_pollable_output_stream_is_writable
                                                        (<em class="parameter"><code><a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> *stream</code></em>);</pre>
<p>
Checks if <em class="parameter"><code>stream</code></em> can be written.
</p>
<p>
Note that some stream types may not be able to implement this 100%
reliably, and it is possible that a call to <a class="link" href="gio-GOutputStream.html#g-output-stream-write" title="g_output_stream_write ()"><code class="function">g_output_stream_write()</code></a>
after this returns <a href="../glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> would still block. To guarantee
non-blocking behavior, you should always use
<a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-write-nonblocking" title="g_pollable_output_stream_write_nonblocking ()"><code class="function">g_pollable_output_stream_write_nonblocking()</code></a>, which will return a
<a class="link" href="gio-GIOError.html#G-IO-ERROR-WOULD-BLOCK:CAPS"><code class="literal">G_IO_ERROR_WOULD_BLOCK</code></a> error rather than blocking.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>stream</code></em> :</span></p></td>
<td>a <a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a>.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>
<a href="../glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> if <em class="parameter"><code>stream</code></em> is writable, <a href="../glib/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> if not. If an error
has occurred on <em class="parameter"><code>stream</code></em>, this will result in
<a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-is-writable" title="g_pollable_output_stream_is_writable ()"><code class="function">g_pollable_output_stream_is_writable()</code></a> returning <a href="../glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a>, and the
next attempt to write will return the error.</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 2.28</p>
</div>
<hr>
<div class="refsect2">
<a name="g-pollable-output-stream-create-source"></a><h3>g_pollable_output_stream_create_source ()</h3>
<pre class="programlisting"><a href="../glib/glib-The-Main-Event-Loop.html#GSource"><span class="returnvalue">GSource</span></a> *           g_pollable_output_stream_create_source
                                                        (<em class="parameter"><code><a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> *stream</code></em>,
                                                         <em class="parameter"><code><a class="link" href="gio-GCancellable.html#GCancellable" title="GCancellable"><span class="type">GCancellable</span></a> *cancellable</code></em>);</pre>
<p>
Creates a <a href="../glib/glib-The-Main-Event-Loop.html#GSource"><span class="type">GSource</span></a> that triggers when <em class="parameter"><code>stream</code></em> can be written, or
<em class="parameter"><code>cancellable</code></em> is triggered or an error occurs. The callback on the
source is of the <a class="link" href="gio-GPollableInputStream.html#GPollableSourceFunc" title="GPollableSourceFunc ()"><span class="type">GPollableSourceFunc</span></a> type.
</p>
<p>
As with <a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-is-writable" title="g_pollable_output_stream_is_writable ()"><code class="function">g_pollable_output_stream_is_writable()</code></a>, it is possible that
the stream may not actually be writable even after the source
triggers, so you should use <a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-write-nonblocking" title="g_pollable_output_stream_write_nonblocking ()"><code class="function">g_pollable_output_stream_write_nonblocking()</code></a>
rather than <a class="link" href="gio-GOutputStream.html#g-output-stream-write" title="g_output_stream_write ()"><code class="function">g_output_stream_write()</code></a> from the callback.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>stream</code></em> :</span></p></td>
<td>a <a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a>.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>cancellable</code></em> :</span></p></td>
<td>a <a class="link" href="gio-GCancellable.html#GCancellable" title="GCancellable"><span class="type">GCancellable</span></a>, or <a href="../glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>. <span class="annotation">[<acronym title="NULL is ok, both for passing and for returning."><span class="acronym">allow-none</span></acronym>]</span>
</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>a new <a href="../glib/glib-The-Main-Event-Loop.html#GSource"><span class="type">GSource</span></a>. <span class="annotation">[<acronym title="Free data after the code is done."><span class="acronym">transfer full</span></acronym>]</span>
</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 2.28</p>
</div>
<hr>
<div class="refsect2">
<a name="g-pollable-output-stream-write-nonblocking"></a><h3>g_pollable_output_stream_write_nonblocking ()</h3>
<pre class="programlisting"><a href="../glib/glib-Basic-Types.html#gssize"><span class="returnvalue">gssize</span></a>              g_pollable_output_stream_write_nonblocking
                                                        (<em class="parameter"><code><a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a> *stream</code></em>,
                                                         <em class="parameter"><code>const <span class="type">void</span> *buffer</code></em>,
                                                         <em class="parameter"><code><a href="../glib/glib-Basic-Types.html#gsize"><span class="type">gsize</span></a> size</code></em>,
                                                         <em class="parameter"><code><a class="link" href="gio-GCancellable.html#GCancellable" title="GCancellable"><span class="type">GCancellable</span></a> *cancellable</code></em>,
                                                         <em class="parameter"><code><a href="../glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> **error</code></em>);</pre>
<p>
Attempts to write up to <em class="parameter"><code>size</code></em> bytes from <em class="parameter"><code>buffer</code></em> to <em class="parameter"><code>stream</code></em>, as
with <a class="link" href="gio-GOutputStream.html#g-output-stream-write" title="g_output_stream_write ()"><code class="function">g_output_stream_write()</code></a>. If <em class="parameter"><code>stream</code></em> is not currently writable,
this will immediately return <a class="link" href="gio-GIOError.html#G-IO-ERROR-WOULD-BLOCK:CAPS"><code class="literal">G_IO_ERROR_WOULD_BLOCK</code></a>, and you can
use <a class="link" href="gio-GPollableOutputStream.html#g-pollable-output-stream-create-source" title="g_pollable_output_stream_create_source ()"><code class="function">g_pollable_output_stream_create_source()</code></a> to create a <a href="../glib/glib-The-Main-Event-Loop.html#GSource"><span class="type">GSource</span></a>
that will be triggered when <em class="parameter"><code>stream</code></em> is writable.
</p>
<p>
Note that since this method never blocks, you cannot actually
use <em class="parameter"><code>cancellable</code></em> to cancel it. However, it will return an error
if <em class="parameter"><code>cancellable</code></em> has already been cancelled when you call, which
may happen if you call this method after a source triggers due
to having been cancelled.
</p>
<p>
Virtual: write_nonblocking
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>stream</code></em> :</span></p></td>
<td>a <a class="link" href="gio-GPollableOutputStream.html#GPollableOutputStream" title="GPollableOutputStream"><span class="type">GPollableOutputStream</span></a>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>buffer</code></em> :</span></p></td>
<td>a buffer to write
data from. <span class="annotation">[<acronym title="Parameter points to an array of items."><span class="acronym">array</span></acronym> length=size][<acronym title="Generics and defining elements of containers and arrays."><span class="acronym">element-type</span></acronym> guint8]</span>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>size</code></em> :</span></p></td>
<td>the number of bytes you want to write</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>cancellable</code></em> :</span></p></td>
<td>a <a class="link" href="gio-GCancellable.html#GCancellable" title="GCancellable"><span class="type">GCancellable</span></a>, or <a href="../glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>. <span class="annotation">[<acronym title="NULL is ok, both for passing and for returning."><span class="acronym">allow-none</span></acronym>]</span>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>error</code></em> :</span></p></td>
<td>
<a href="../glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> for error reporting, or <a href="../glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> to ignore.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>the number of bytes written, or -1 on error (including
<a class="link" href="gio-GIOError.html#G-IO-ERROR-WOULD-BLOCK:CAPS"><code class="literal">G_IO_ERROR_WOULD_BLOCK</code></a>).</td>
</tr>
</tbody>
</table></div>
</div>
</div>
<div class="refsect1">
<a name="gio-GPollableOutputStream.see-also"></a><h2>See Also</h2>
<a class="link" href="gio-GOutputStream.html#GOutputStream" title="GOutputStream"><span class="type">GOutputStream</span></a>, <a class="link" href="gio-GFileDescriptorBased.html#GFileDescriptorBased" title="GFileDescriptorBased"><span class="type">GFileDescriptorBased</span></a>, <a class="link" href="gio-GPollableInputStream.html#GPollableInputStream" title="GPollableInputStream"><span class="type">GPollableInputStream</span></a>
</div>
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